Typical page in its source form may contain both graphical and image elements.
A graphical element is usually characterized as being in the form of vector-based data, which defines the exact shape and position of the graphical element on a printed material. For example, fonts are usually classified as graphical data. Line art is another example of graphical data.
Image data, on the other hand, is typically raster data in a specific resolution, represented in a bitmap format (in many instances it may be represented in a compressed format, for example, JPEG). Typically, the source of the image data is an image capturing device such as digital camera or a scanner.
A RIP (raster image processing) software application is used to put together graphical and image elements on a page in its source form. The RIP application then rasters and flattens the graphical and image elements according the printing device resolution and color planes (typically CMYK).
At this point trapping may be performed. Trapping is done on the graphical edges according to their rendered CMYK mix. The RIP application may easily do it, as it already has information on the location of graphical edges. The page is than sent to a printer, printed and reviewed. According to the result, the operator may decide to add or change image enhancement (e.g. sharpening) or trapping parameters. In this case the page is returned back to the enhancement and authoring tools and the RIP module—all of which are time and resource consuming.
Trapping and image enhancement require the RIP application to have the ability and knowledge to parse the specific format of the page (e.g. PDF, Postscript). Furthermore, it is advantageous to know the printing properties of the specific printer on which the specific page is to be printed, and in particular the actual misregistration properties of that specific printer, for successful trapping.
However many times the editor of the page cannot anticipate on which printer the page will eventually be printed, nor has any control of that printer. In other cases, the editor is not an expert in printing and is not aware of the potential misregistration effect. Such an inexperienced user may choose color schemes that are inherently susceptible to misregistration,
Thus misregistration artifacts are widely found in many printed pages. Misregistration is usually more noticeable when occurring at the location of graphical elements on the page, but beyond a visible threshold it may also be visible on the image parts of the page. On the other hand, if trapping is carried out on a page with image elements this alone can cause artifacts to appear on the image elements.